Celiac disease is characterized by small intestinal mucosal injury and the malabsorption of most nutrients. Disease is activated by the dietary ingestion of wheat gliadin and similar alcohol soluble proteins in other grains. Disease susceptibility is associated with a specific HLA class II molecule (i.e., a DQw2 heterodimer) that is encoded by the DQA1*0501 and DQB1*0201 alleles. T cells play an important role in the activation nd perpetuation of disease. Differences in the level of expression of the disease associated DQ molecule relative to other HLA class II D region molecules, or differences in its pattern of tissue specific expression during ontogeny may be a critical factor in determining disease susceptibility. We have defined polymorphisms in the 5' regulatory region of the celiac disease associated DQA1*0501 allele relative to other DQA1 alleles. Using chimeric reporter gene constructs and DQA1*0501 transgenic mice, the first Aim of these studies will test the hypothesis that these polymorphisms determine the level of expression of DQA1*0501 relative to other DQA1 alleles or its tissue specific pattern of expression during ontogeny. The specific peptide(s) of gliadin that activate disease have not been precisely defined. Therefore, a second Aim of these studies is to identify the endogenously processed peptides of gliadin that are ligands for the human HLA DQw2 heterodimer associated with celiac disease. These experiments will isolate DQw2 molecules that contain endogenously processed gliadin from transfected cell lines that express only the DQw2 molecule and, in collaboration, determine the amino acid sequence of those peptides by HPLC and mass spectroscopy. The third Aim of these studies is to characterize the specific T cell populations in celiac disease patients that are important in the pathogenesis of this disease. These studies will use a combination of molecular approaches a) to define the alpha/beta and gamma/delta V genes used by T cell receptors that are present in the celiac disease lesion of patients in remission and patients with active disease, and to define the repertoire and clonality of these receptors; b) to define the T cell receptors that recognize the DQw2-gliadin peptide complex defined in Aim 2; and c) to characterize the T cell receptors that are important in disease pathogenesis in the early period after the activation of disease by in vivo challenge with gliadin peptides. New information derived from these studies will help to define the specific mechanisms by which specific HLA genes, gliadin peptides and T cells contribute to the pathogenesis of celiac disease, and point to new strategies for the prevention and treatment of this disease.